Interface ModuleFinder

A ModuleFinder can only find one module with a given name. A
ModuleFinder that finds modules in a sequence of directories, for
example, will locate the first occurrence of a module of a given name and
will ignore other modules of that name that appear in directories later in
the sequence.

The find and findAll methods
defined here can fail for several reasons. These include I/O errors, errors
detected parsing a module descriptor (module-info.class), or in the
case of ModuleFinder returned by ModuleFinder.of, that
two or more modules with the same name are found in a directory.
When an error is detected then these methods throw FindException with an appropriate cause.
The behavior of a ModuleFinder after a FindException is
thrown is undefined. For example, invoking find after an exception
is thrown may or may not scan the same modules that lead to the exception.
It is recommended that a module finder be discarded after an exception is
thrown.

Method Detail

find

A ModuleFinder provides a consistent view of the
modules that it locates. If find is invoked several times to
locate the same module (by name) then it will return the same result
each time. If a module is located then it is guaranteed to be a member
of the set of modules returned by the findAll
method.

Parameters:

name - The name of the module to find

Returns:

A reference to a module with the given name or an empty
Optional if not found

findAll

A ModuleFinder provides a consistent view of the modules
that it locates. If findAll is invoked several times
then it will return the same (equals) result each time. For each
ModuleReference element in the returned set then it is guaranteed that
find will locate the ModuleReference if invoked
to find that module.

API Note:

This is important to have for methods such as resolveAndBind that need to scan the
module path to find modules that provide a specific service.

of

Returns a module finder that locates modules on the file system by
searching a sequence of directories and/or packaged modules.
Each element in the given array is one of:

A path to a directory of modules.

A path to the top-level directory of an
exploded module.

A path to a packaged module.

The module finder locates modules by searching each directory, exploded
module, or packaged module in array index order. It finds the first
occurrence of a module with a given name and ignores other modules of
that name that appear later in the sequence.

If an element is a path to a directory of modules then each entry in
the directory is a packaged module or the top-level directory of an
exploded module. It is an error if a directory contains more than one
module with the same name. If an element is a path to a directory, and
that directory contains a file named module-info.class, then the
directory is treated as an exploded module rather than a directory of
modules.

The module finder returned by this method
supports modules packaged as JAR files. A JAR file with a
module-info.class in its top-level directory, or in a versioned entry
in a multi-release
JAR file, is a modular JAR file and thus defines an explicit
module. A JAR file that does not have a module-info.class in its
top-level directory defines an automatic module, as follows:

If the JAR file has the attribute "Automatic-Module-Name"
in its main manifest then its value is the module name. The module name is otherwise
derived from the name of the JAR file.

The version, and the
module name when the attribute "Automatic-Module-Name" is not
present, are derived from the file name of the JAR file as follows:

The ".jar" suffix is removed.

If the name matches the regular expression
"-(\\d+(\\.|$))" then the module name will be derived from the
subsequence preceding the hyphen of the first occurrence. The
subsequence after the hyphen is parsed as a Version and ignored if it cannot be
parsed as a Version.

All non-alphanumeric characters ([^A-Za-z0-9])
in the module name are replaced with a dot ("."), all
repeating dots are replaced with one dot, and all leading and
trailing dots are removed.

As an example, a JAR file named "foo-bar.jar" will
derive a module name "foo.bar" and no version. A JAR file
named "foo-bar-1.2.3-SNAPSHOT.jar" will derive a module
name "foo.bar" and "1.2.3-SNAPSHOT" as the version.

The set of packages in the module is derived from the
non-directory entries in the JAR file that have names ending in
".class". A candidate package name is derived from the name
using the characters up to, but not including, the last forward slash.
All remaining forward slashes are replaced with dot ("."). If
the resulting string is a legal package name then it is assumed to be
a package name. For example, if the JAR file contains the entry
"p/q/Foo.class" then the package name derived is
"p.q".

The contents of entries starting with
META-INF/services/ are assumed to be service configuration files
(see ServiceLoader). If the name of a file
(that follows META-INF/services/) is a legal class name
then it is assumed to be the fully-qualified class name of a service
type. The entries in the file are assumed to be the fully-qualified
class names of provider classes.

If the JAR file has a Main-Class attribute in its
main manifest, its value is a legal class name, and its package is
in the set of packages derived for the module, then the value is the
module main class.

If a ModuleDescriptor cannot be created (by means of the
ModuleDescriptor.Builder API) for an
automatic module then FindException is thrown. This can arise
when the value of the "Automatic-Module-Name" attribute is not a
legal module name, a legal module name cannot be derived from the file
name of the JAR file, where the JAR file contains a .class in
the top-level directory of the JAR file, where an entry in a service
configuration file is not a legal class name or its package name is not
in the set of packages derived for the module.

In addition to JAR files, an implementation may also support modules
that are packaged in other implementation specific module formats. If
an element in the array specified to this method is a path to a directory
of modules then entries in the directory that not recognized as modules
are ignored. If an element in the array is a path to a packaged module
that is not recognized then a FindException is thrown when the
file is encountered. Paths to files that do not exist are always ignored.

As with automatic modules, the contents of a packaged or exploded
module may need to be scanned in order to determine the packages
in the module. Whether hidden files are ignored or not is implementation specific and therefore
not specified. If a .class file (other than
module-info.class) is found in the top-level directory then it is
assumed to be a class in the unnamed package and so FindException
is thrown.

Finders created by this method are lazy and do not eagerly check
that the given file paths are directories or packaged modules.
Consequently, the find or findAll methods will only
fail if invoking these methods results in searching a directory or
packaged module and an error is encountered.

Parameters:

entries - A possibly-empty array of paths to directories of modules
or paths to packaged or exploded modules

Returns:

A ModuleFinder that locates modules on the file system

compose

Returns a module finder that is composed from a sequence of zero or more
module finders. The find method of the resulting
module finder will locate a module by invoking the find method
of each module finder, in array index order, until either the module is
found or all module finders have been searched. The findAll method of the resulting module finder will return a set of
modules that includes all modules located by the first module finder.
The set of modules will include all modules located by the second or
subsequent module finder that are not located by previous module finders
in the sequence.

When locating modules then any exceptions or errors thrown by the
find or findAll methods of the underlying module finders
will be propagated to the caller of the resulting module finder's
find or findAll methods.